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Richard J. Delahay

Other affiliations: Central Science Laboratory, Shire plc, University of Exeter  ...read more
Bio: Richard J. Delahay is an academic researcher from Animal and Plant Health Agency. The author has contributed to research in topics: Meles & Badger. The author has an hindex of 48, co-authored 190 publications receiving 7488 citations. Previous affiliations of Richard J. Delahay include Central Science Laboratory & Shire plc.


Papers
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Journal ArticleDOI
TL;DR: This paper reviews field methods for estimating and monitoring the abundance of terrestrial carnivores that do not involve capture and a variety of approaches based on direct observations and quantification of field signs are employed.
Abstract: This paper reviews field methods for estimating and monitoring the abundance of terrestrial carnivores that do not involve capture. Effective methods of monitoring abundance are important tools for the management and conservation of many species. The development of methods for carnivores presents particular challenges, as they are often secretive and widely dispersed. Nevertheless, a variety of approaches based on direct observations and quantification of field signs have been employed. These techniques are described in relation to carnivore ecology and resource implications, and the advantages and deficiencies of each are discussed with reference to case studies. Estindasvore G.ls J W033 Ga J. Rlah

330 citations

Journal ArticleDOI
TL;DR: In a study of 53 faeces sampled from three social groups over 10 days, it is found that direct enumeration could not be used to estimate population size, but that the application of mark–recapture models has the potential to provide more accurate results.
Abstract: The potential link between badgers and bovine tuberculosis has made it vital to develop accurate techniques to census badgers. Here we investigate the potential of using genetic profiles obtained from faecal DNA as a basis for population size estimation. After trialling several methods we obtained a high amplification success rate (89%) by storing faeces in 70% ethanol and using the guanidine thiocyanate/silica method for extraction. Using 70% ethanol as a storage agent had the advantage of it being an antiseptic. In order to obtain reliable genotypes with fewer amplification reactions than the standard multiple-tubes approach, we devised a comparative approach in which genetic profiles were compared and replication directed at similar, but not identical, genotypes. This modified method achieved a reduction in polymerase chain reactions comparable with the maximum-likelihood model when just using reliability criteria, and was slightly better when using reliability criteria with the additional proviso that alleles must be observed twice to be considered reliable. Our comparative approach would be best suited for studies that include multiple faeces from each individual. We utilized our approach in a well-studied population of badgers from which individuals had been sampled and reliable genotypes obtained. In a study of 53 faeces sampled from three social groups over 10 days, we found that direct enumeration could not be used to estimate population size, but that the application of mark-recapture models has the potential to provide more accurate results.

281 citations

Journal ArticleDOI
TL;DR: It is demonstrated that culling badgers profoundly alters their spatial organization as well as their population density, which has the potential to influence contact rates between cattle and badgers, both where culls occur and on adjoining land.
Abstract: 1. The incidence of bovine tuberculosis (TB) in British cattle has risen markedly over the last two decades. Failure to control the disease in cattle has been linked to the persistence of a reservoir of infection in European badgers Meles meles, a nationally protected species. Although badger culling has formed a component of British TB control policy for many years, a recent large-scale randomized field experiment found that TB incidence in cattle was no lower in areas subject to localized badger culling than in nearby areas where no experimental culls occurred. Indeed, analyses indicated that cattle incidence was higher in culled areas. 2. One hypothesis advanced to explain this pattern is that localized culling disrupted badgers' territorial behaviour, potentially increasing the rate of contact between cattle and infected badgers. This study evaluated this hypothesis by investigating badger activity and spatial organization in 13 study areas subjected to different levels of culling. Badger home ranges were mapped by feeding colour-marked baits at badger dens and measuring the geographical area in which colour-marked faeces were retrieved. 3. Badger home ranges were consistently larger in culling areas. Moreover, in areas not subjected to culling, home range sizes increased with proximity to the culling area boundary. Patterns of overlap between home ranges were also influenced by culling. 4. Synthesis and applications. This study demonstrates that culling badgers profoundly alters their spatial organization as well as their population density. These changes have the potential to influence contact rates between cattle and badgers, both where culls occur and on adjoining land. These results may help to explain why localized badger culling appears to have failed to control cattle TB, and should be taken into account in determining what role, if any, badger culling should play in future control strategies.

193 citations

Journal ArticleDOI
TL;DR: The distribution of disease reflects stable persistent foci of infection in the badger population, with limited evidence of transfer between social groups, and would allow a range of management strategies for the control of bovine TB to be efficiently targeted in such populations.
Abstract: Summary 1. The European badger (Meles meles) is implicated as a reservoir of Mycobacterium bovis (bovine TB) infection for cattle in Britain and Ireland. In the present study the spatio-temporal distribution of M. bovis infection was investigated. Analyses were carried out on data from a long-term epidemiological and ecological study of the dynamics of bovine TB in a wild population of badgers at Woodchester Park in south-west England. 2. During the 15 years of the capture–mark–recapture study (1982–96), 3316 trapping and post-mortem records were obtained from 1270 individual badgers. Annual prevalence of infection based on positive serological and bacterial tests varies between 10·3% and 17·7% of the population. 3. Infection was aggregated in social groups in the west of the study area, confirming the findings of previous studies. However, temporal trends in disease were not synchronized amongst neighbouring groups, suggesting low rates of disease transfer between them. 4. There was significant serial correlation in the disease status within groups over time, suggesting that infection persists for many years in some social groups. The presence of infectious adult female badgers in groups was associated with new infections, and provides further evidence for their importance in the maintenance of infection within groups. However, no statistically significant correlations were detected between the demographic characteristics of social groups and group infection status. 5. The distribution of disease reflects stable persistent foci of infection in the badger population, with limited evidence of transfer between social groups. The accurate identification of stable foci of infection would allow a range of management strategies for the control of bovine TB to be efficiently targeted in such populations. However, the extent to which this pattern of infection is representative of low-density and disturbed badger populations is unknown.

182 citations

Journal ArticleDOI
TL;DR: In this article, Saez et al. made valuable comments on the first draft PA is currently holding a Juan de la Cierva research contract awarded by the Ministerio de Ciencia e Innovacion-Fondo Social Europeo.
Abstract: The current study is a contribution to Junta de Comunidades de Castilla-La Mancha (JCCM) PPIC10-0226-0243, Ministerio de Ciencia e Innovacion (MCINN) Plan Nacional I + D + i AGL2008-03875 and Fondo Europeo de Desarrollo Regional (FEDER) and to FP7 EU TB-STEP (212414) (Strategies for the eradication of bovine tuberculosis) Studies on diseases shared between domestic animals and wildlife are also supported by Santander and Fundacion Marcelino Botin Jose Luis Saez (Ministerio de Medio Ambiente, Rural y Marino, MARM) made valuable comments on the first draft PA is currently holding a Juan de la Cierva research contract awarded by the Ministerio de Ciencia e Innovacion – Fondo Social Europeo

178 citations


Cited by
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Proceedings ArticleDOI
22 Jan 2006
TL;DR: Some of the major results in random graphs and some of the more challenging open problems are reviewed, including those related to the WWW.
Abstract: We will review some of the major results in random graphs and some of the more challenging open problems. We will cover algorithmic and structural questions. We will touch on newer models, including those related to the WWW.

7,116 citations

01 Jan 1980
TL;DR: In this article, the influence of diet on the distribution of nitrogen isotopes in animals was investigated by analyzing animals grown in the laboratory on diets of constant nitrogen isotopic composition and found that the variability of the relationship between the δ^(15)N values of animals and their diets is greater for different individuals raised on the same diet than for the same species raised on different diets.
Abstract: The influence of diet on the distribution of nitrogen isotopes in animals was investigated by analyzing animals grown in the laboratory on diets of constant nitrogen isotopic composition. The isotopic composition of the nitrogen in an animal reflects the nitrogen isotopic composition of its diet. The δ^(15)N values of the whole bodies of animals are usually more positive than those of their diets. Different individuals of a species raised on the same diet can have significantly different δ^(15)N values. The variability of the relationship between the δ^(15)N values of animals and their diets is greater for different species raised on the same diet than for the same species raised on different diets. Different tissues of mice are also enriched in ^(15)N relative to the diet, with the difference between the δ^(15)N values of a tissue and the diet depending on both the kind of tissue and the diet involved. The δ^(15)N values of collagen and chitin, biochemical components that are often preserved in fossil animal remains, are also related to the δ^(15)N value of the diet. The dependence of the δ^(15)N values of whole animals and their tissues and biochemical components on the δ^(15)N value of diet indicates that the isotopic composition of animal nitrogen can be used to obtain information about an animal's diet if its potential food sources had different δ^(15)N values. The nitrogen isotopic method of dietary analysis probably can be used to estimate the relative use of legumes vs non-legumes or of aquatic vs terrestrial organisms as food sources for extant and fossil animals. However, the method probably will not be applicable in those modern ecosystems in which the use of chemical fertilizers has influenced the distribution of nitrogen isotopes in food sources. The isotopic method of dietary analysis was used to reconstruct changes in the diet of the human population that occupied the Tehuacan Valley of Mexico over a 7000 yr span. Variations in the δ^(15)C and δ^(15)N values of bone collagen suggest that C_4 and/or CAM plants (presumably mostly corn) and legumes (presumably mostly beans) were introduced into the diet much earlier than suggested by conventional archaeological analysis.

5,548 citations

30 Apr 1984
TL;DR: A review of the literature on optimal foraging can be found in this article, with a focus on the theoretical developments and the data that permit tests of the predictions, and the authors conclude that the simple models so far formulated are supported by available data and that they are optimistic about the value both now and in the future.
Abstract: Beginning with Emlen (1966) and MacArthur and Pianka (1966) and extending through the last ten years, several authors have sought to predict the foraging behavior of animals by means of mathematical models. These models are very similar,in that they all assume that the fitness of a foraging animal is a function of the efficiency of foraging measured in terms of some "currency" (Schoener, 1971) -usually energy- and that natural selection has resulted in animals that forage so as to maximize this fitness. As a result of these similarities, the models have become known as "optimal foraging models"; and the theory that embodies them, "optimal foraging theory." The situations to which optimal foraging theory has been applied, with the exception of a few recent studies, can be divided into the following four categories: (1) choice by an animal of which food types to eat (i.e., optimal diet); (2) choice of which patch type to feed in (i.e., optimal patch choice); (3) optimal allocation of time to different patches; and (4) optimal patterns and speed of movements. In this review we discuss each of these categories separately, dealing with both the theoretical developments and the data that permit tests of the predictions. The review is selective in the sense that we emphasize studies that either develop testable predictions or that attempt to test predictions in a precise quantitative manner. We also discuss what we see to be some of the future developments in the area of optimal foraging theory and how this theory can be related to other areas of biology. Our general conclusion is that the simple models so far formulated are supported are supported reasonably well by available data and that we are optimistic about the value both now and in the future of optimal foraging theory. We argue, however, that these simple models will requre much modification, espicially to deal with situations that either cannot easily be put into one or another of the above four categories or entail currencies more complicated that just energy.

2,709 citations

Journal ArticleDOI

1,148 citations

Journal ArticleDOI
TL;DR: There is potential for the restoration of apex predators to have benefits for biodiversity conservation through moderation of the impacts of mesopredators on their prey, but this requires a whole-ecosystem view to avoid unforeseen negative effects.
Abstract: There is growing recognition of the important roles played by predators in regulating ecosystems and sustaining biodiversity. Much attention has focused on the consequences of predator-regulation of herbivore populations, and associated trophic cascades. However apex predators may also control smaller 'mesopredators' through intraguild interactions. Removal of apex predators can result in changes to intraguild interactions and outbreaks of mesopredators ('mesopredator release'), leading in turn to increased predation on smaller prey. Here we provide a review and synthesis of studies of predator interactions, mesopredator release and their impacts on biodiversity. Mesopredator suppression by apex predators is widespread geographically and taxonomically. Apex predators suppress mesopredators both by killing them, or instilling fear, which motivates changes in behaviour and habitat use that limit mesopredator distribution and abundance. Changes in the abundance of apex predators may have disproportionate (up to fourfold) effects on mesopredator abundance. Outcomes of interactions between predators may however vary with resource availability, habitat complexity and the complexity of predator communities. There is potential for the restoration of apex predators to have benefits for biodiversity conservation through moderation of the impacts of mesopredators on their prey, but this requires a whole-ecosystem view to avoid unforeseen negative effects. 'Nothing has changed since I began. My eye has permitted no change. I am going to keep things like this.' From 'Hawk Roosting', by Ted Hughes.

1,021 citations